It is necessary for all travellers to ensure that they have the correct documentation for boarding their cruise and for entering each country where the ship stops.  If you do not have the correct documentation then you may be prevented from entering one of the intended destinations or from boarding the ship itself. 

When you book your cruise you will be given details of all required documentation.  Immigration laws for some countries may require that you have a certain amount of time left to run on your passport, for example, and some countries may require evidence that certain vaccinations are up to date.  It may be necessary to apply for tourist visas for some countries, even though the visit may be less than a day. 

For US citizens who are simply cruising around the Americas, it may be that not even a passport is required, although this does depend upon the destination and advice can be obtained from your cruise co-ordinator.  It is a good idea to carry a passport in case some form of identification is required.  Europeans who are cruising around the Mediterranean may need nothing more than a passport, but this does depend on individual stops and again, detailed information should be provided by the travel agent before you sail. 

If you choose to take a Far East cruise, then it may be that some vaccinations are required.  It is a good idea to check with the nation’s embassy in your home country to establish what the current requirements are.